Steam generating unit



Filed March 14, 1961 4 Sheets-Sheet l INVENT OR GEORGE PARMA KIA N ATTORNEY FIG. I.

July 2, 1963 G. PARMAKIAN STEAM GENERATING UNIT 4 Sheets-Sheet 2 Filed March 14, 1961 FIG. 2

FIG. 3.

GEORGE PARMAK/AN" INVENTOR ATTORNEY y 1963 G. PARMAKIAN 3,095,863

STEAM GENERATING UNIT Filed March 14, 1961 4 Sheets-*She et a FIG. 5.

FIG. 4.

INVENIOR ZTTORNEY July 2, 1963 e. PARMAKIAN STEAM GENERATING mm 4 Sheets-Sheet; 4

Filed March 14, 1961 u E H R E W a D LOAD meow? FIG. 7.

United States Filed Mar. 14, 1961, Ser. No. 95,675 3 Claims. or. 122-479 This invention relates to a steam generating unit and more particularly to apparatus arranged to regulate the temperature of superheated steam in a boiler.

In the generation of steam for use in producing electricity by means of a turbine, it is very necessary that the temperature of the steam reaching the turbine be maintained at a pre-determined value with very little variation. Otherwise, the turbine will not operate at full efficiency. Furthermore, in present-day steam generating units, the temperature of the steam is very close to the failure point of the metal in the superheater tube and strict regulation is necessary to amure that the temperature of the superheat does not go above the design value and cause tube failure. One of the methods commonly used for regulating the temperature of superheated steam is that of recirculation of gas through the main furnace from the back passes of the boiler. The effect of this recirculation is to cool the gases passing over the convection surfaces and also to increase the mass flow. Generally speaking, an increase in mass flow dominates the situation and the temperature goes up, despite the fact that the temperature of the gases passing over the superheater surfaces in lower. Because of the fact that the recirculated gas is used in considerably greater amounts at low loads where an increase in the temperature of superheated steam is more necessary, a number of problems are presented. First of all, since the normal products of combustion are smaller in amount at low loads, they do not mix as thoroughly with the recirculated gas which has been introduced into the furnace as at high loads. There are difiiculties with ignition, for instance, and also in providing a suitable place for the introduction of the recirculated gas. These and other difiiculties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a novel apparatus for the control of superheat by the recirculation of gas.

Another object of this invention is the provision of a steam generating unit making use of the recirculation of gas from the back passes to the main furnace in which gas temperature from side to side of the furnace are maintained substantially uniform.

It is another object of the instant invention to provide a superheat control in which the recirculated gas is very thoroughly mixed with the ordinary products of combustion before passage through the boiler.

It is a further object of the invention to provide a steam generating unit embodying a novel method of introducing recirculated gas.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical longitudinal view of a steam generating unit embodying the principles of the present invention;

FIG. 2 is a view of the furnace taken along the line II-II of FIG. 1;

FIG. 3 is a sectional view of the invention taken along the line III-1H of FIG. 2;

FIG. 4 is a sectional view of the invention taken along the line IV-IV of FIG. 2;

FIG. 5 is a sectional view of the invention taken along the line VV of FIG. 2;

FIG. 6 is a graph showing the variation of superheat temperature with changes in load; and

FIG. 7 is a graph showing various relationships of reheat and load.

Referring first to FIG. 1, which best shows the general features of the invention, the steam generating unit, indicated generally by the reference numeral 10, is shown as consisting of a furnace 11 and a boiler 12. The steam generating unit is mounted on a supporting structure 13. The furnace 11 is provided with a front wall 14, a rear wall 15, and side walls :16 defining a vertically-elongated combustion chamber 17. The furnace is of the type generally shown and described in the patent of Craig #2,853,059 and is provided with a continuous slag bottom 18. The front wall 14 is provide with an abutment 19 which extends inwardly of the furnace; the abutment has an inclined upper surface 21 and a similarly inclined lower surface 22. The rear wall 15 is provided with a similar abutment 23 having an inclined upper surface 24 and an inclined lower surface 25. The inclined lower surfaces of the two abutments are provided with directional-flame intertube burners 26 and 27 of the type shown in the patent to Craig #2,759,460 which are connected in the usual way with sources of air and fuel. The abutments 19 and 23 extend in opposition to each other across the combustion chamber and divide the combustion chamber into a lower portion 28 and an upper portion 29. The boiler 12, which cooperates with the furnace 11 in the usual way, consists of a steam-and-water drum 31 from which radiate the various tubes of the boiler system. Large d-owncorner tubes (not shown) carry the water to the lower portion of the boiler and this flows upwardly through the system, particularly in Water-wall tubes 20 which lie in the surface of the combustion chamber 17. These water-wall tubes particularly cover the surfaces of the abutments l9 and 23. The directionahfiame burners 26 and 27 are so arranged that the fuel and combustion air passes through gaps provided between certain of the water-wall tubes. Steam generated in the water-wall tubes 20 is introduced into the steam-and-Water wall drum 31. At the upper part of the steam-and-water drum are tubes 32 leading to a primary or low-temperature superheater 33. The outlet end of the low-temperature superheater 33 is connected to a secondary or high-temperature superheater 34, the outlet of which is connected to the turbine (not shown) in the usual manner.

The steam generating unit is provided with a back pass 35 divided by a wall 36 into a forward pass 37 and a rearward pass 38. The low-temperature superheater 33 is located in the rearward pass 38 and the low-temperature reheater 39 is located in the forward pass 37. At the upper portion of this combustion chamber 17 the rearward wall 15 is inclined forwardly to form a nose 41 defining a short horizontal upper pass 42. A high-temperature reheater 43 resides in this upper pass as does the terminal portion of the high-temperature superheater 34. The major portion of the high-temperature superheater 34, however, resides in the upper portion of the combustion chamber 17 and consists of large pendant platens. The lower ends of the platens of the high-temperature superheater 34 extend below the nose 41 into the upper part of the combustion chamber.

In the lower portion of the rearward pass 38 are located dampers 44 which control the flow of gas therethrough. These dampers are connected to an actuating rod 45 so as to operate together and the rod 45 is connected to a linear actuator, such as a hydraulic cylinder 46. Hydraulic lines 47 and 48 lead to a main control 49 and are connected to the cylinder. The said main control 49 is similar to that shown and described in the co-pending patent application of Parmakian Serial Number 774,074, filed November 14, 1958. In the lower end of the ior ward pass 37 are located dampers 51 which are mova-ble together under the action of a rod 52 connected to a hydraulic cylinder 53 which operates under the control of hydraulic lines 54 and 55 connected to the main control 49. I p i The lower end of the back pass 35 of the steam generating unit is connected through an air heater 56 to a breaching 57 which leads to a stack (not shown). The outlet of the low-temperature reheater 33 is connected to a reheated steam header 58, while the outlet of the high temperature superheater 34 is connected to a superheated steam header 59.

The lower surface of the abutment 19 is formed with a series of openings between pairs of the burners 26. These openings are formed by displacing water-wall tubes to form passages between the burners. A similar series of openings is formed between pairs of the burners 27 on the undersurface of the abutment 23. A large conduit 61 is connected to the openings on the abutment 19, while a similar conduit 62 is connected to the openings on the under side of the abutment 23. The conduits 61 and 62 merge to form a single conduit 65 having mounted therein a regulating damper 66. The end of the conduit 65 which is away from the connection to the conduits 6-1 and 62 is connected to the outlet of the fan 67. The inlet of the fan 67 is connected by :a conduit 68 through a back pass, such as the portion of the steam generating unit lying between the dampers 44 and 51 on the one hand and the air heater 56 on the other hand.

The damper 66 is pivotally mounted and is actuated through rods 69 and 71, the latter rods being connected through a hydraulic cylinder 72, whose linear position is determined by the fluid pressure hydraulic lines 73 and 74 connected to the main control 49. The main control is connected through a line 75 to a temperature-indicating device such as the thermocouple 76 located in the superheated steam header 59. The main control 49 is connected in a similar manner by a line 77 to a temperatureindicating device such as the thermocouple 78 lying in the reheated steam header 58.

FIG. 2 shows the manner in which the burners 26 are alternately located with recirculated gas openings 79. Both the burner openings and the recirculated gas openings are provided by bending back certain of the water- Wall tubes 20. The manner in which this is accomplished is best shown in FIG. 3 where a burner 26 is formed by bending four groups of three tubes back into a plane at a right angle to the surface of thefront wall. In a similar manner the recirculated gas opening 79 is formed by bending back tubes to form groups of threes. A small number of tubes are left in the wall between the burners and gas openings. A typical burner 26 is shown in FIG. 4. A main fuel gun 81 extends centrally of the burner and is connected to a conduit 82 from which it receives the powdered coal and air. A gas 83 is located centrally of the main fuel gun for maintaining ignition and igniter 84 is located in the burner closely adjacent the main fuel gun, the igniter being of the electric spark variety and using gas as its fuel. Arranged along the burner above the gun 81 are vanes 85 whose inclination to the horizontal is adjustable by means of a control rod 86. In the lower part of the burner, vanes 87 are controlled by a rod 88. Air arrives at the burner through a duct 89.

Referring now to FIG. 5, which shows a typical recirculated gas opening 79, it can be seen that the tubes 20 have been bent back to form a generally lozengeshaped opening which is lined with refractory 91. A

duct 92 extends inwardly to each burner from the main conduit 61, while the recirculated gas openings on the other side of the burners are connected to the main conduit 62, both of these last-named conduits extending parallel to the side and rear walls of the furnace outside of the line of air plenum chambers associated with the main fuel burners. Associated with each recirculated gas opening is a series of vanes 93 which are pivotally mounted for rotation about a horizontal axis and controllable by a rod 94.

The operation of the invention will now be readily un derstood in View of the above description. Fuel and air leave the burners 26 and 27 and enter lower portion 28 of the combustion chamber 17. The lower portion 28 constitutes a high-temperature cell because of the restricted exit between the abutments 19 and 23 and the temperature in the portion 28 reaches a very high value. Extreme turbulence takes place because of the opposed condition of the burners and because of the presence in the cell of a pool of molten slag which accumulates on the bottom of the furnace. A considerable portion of the combustion takes place in the portion 28 and, because of the high temperature, the formation of slag takes place almost completely in this high-temperature cell and is persuaded to stay there. The products of combustion pass upwardly through the combustion chamber 17 and a certain amount of combustion takes place in the upper portion 2'9. The products of combustion leave the upper portion of the combustion chamber, pass through the horizontal pass 42, and then pass downwardly through the back pass 35. The amounts passing through the forward portion 47 and the rearward portion 48 of the back pass are determined by the settings of the dampers 44 and 51. Gases pass through the air heater 56 into the breaching 57 and then flow into the stack. Heat absorbed by the water-walls of the furnace brings about the generation of steam; this steam enters the steam-and-water drum and, after suitable cleaning in the usual manner, passes downwardly into the lower portion of the primary 'or low-temperature snperheater 33, passing upwardly therethr-ough in counter-flow to the flow of gases. After being superheated in this manner to a certain degree, the steam then passes into the secondary or high-temperature superheater 34, entering the portion thereof adjacent the front wall 14 of the furnace 11. The steam in the high temperature superheater is first subjected to a considerable amount of radiation because of the fact that most of this superheater is in the form of platens which extend deeply into the main combustion chamber 17. The steam is then subjected to a small degree of convection superheating, passes into the superheated steam header 59, and flows from there to the turbine (not shown).

After passing through the high-pressure section of the turbine the steam returns to the boiler for reheating.- It enters the primary reheat section 39 in the lower portion and passes upwardly therethrough in counterfiow to the flow of gases in the forward portion 37 of the back pass. Eventually, the steam reaches the high-temperature section 33 of the reheater, passes forwardly into horizontal pass 42 in counterflow to the flow of gases therethrough, and eventually enters the reheated steam header S8 for passage through the low-pressure section of the turbine. The superheat and reheat temperatures can be controlled in the usual way by regulating a portion of the total amount of products of combustion which pass through the forward portion 37 or the rearward portion 38 of the backpass. The regulation of dampers 3'4 and 5-1 accomplishes this purpose. It is not possible, however, to accomplish complete control of these values by this means alone. By properly setting the damper 66 a certain amount of the products of combustion are carried back into the furnace. These products leave the back passes of the furnace through the conduit 68 under the impetus of the fan 67 and enter the conduit 65. They are then divided between the conduits 61 and 62 and enter the furnace through the openings 79 on the lower surfaces of the abutments 19 and 23. The introduction of large amounts of gas which have been recirculated in this manner has the effect of increasing the mass flow of gases over the heat exchange unit in the boiler. With respect to the convection sections of a heat exchanger, an increase in mass flow (even though this increase is brought about by the introduction of lower temperature gases), results in a greater amount of heat transfer and a raising of the temperature of steam flowing within the heat exchanger. Ordinarily, of course, the recirculation of gas would be reserved only for those portions of load in which substantial increases in superheat and reheat are necessary. Referring to FIGS. 6 and 7, which show the relationship of the superheat temperature and reheat temperature throughout various loads and under various types of furnace operation, let us suppose that the dampers 44, 51, and 66 are such that the preselected value of reheat and superheat are met. If the load is lowered, that is to say, if the demands of the turbine for quantities of steam is reduced, the firing rate of the burners 26 and 27 is also reduced. This means that there is less gas flow and perhaps lower gas temperatures throughout the furnace and boiler. The superheat and reheat will drop, and this will be indicated by the temperature indicating thermocouples 76 and 78 which will transmit signals through the lines 75 and 77, respectively, to the main control 49. Throttling the dampers together will not bring about a raise in reheat and superheat, so that it is necessary to go to another means. The main control 49 senses that damper control will do nothing to raise the reheat and superheat together for its operates through the hydraulic lines 73 and 74 to actuate the hydraulic cylinder 72. The cylinder works through the rods 71 and 69 to reset the damper 66. The resetting in this case will be in the direction of opening the damper and causing a greater amount of recirculated gas to flow into the furnace. The increase in mass flow thus accomplished will raise both the reheat and the superheat. If one or the other of the two temperatures varies from the preselected value, which is indicated on the graphs as being 1,000 E, the main control will operate through hydraulic lines 47, 48, 54, and 55 to move the hydraulic cylinders 46 and 53 to reset the dampers 44 and 51, re spectively. For instance, if reheat is adequate but superheat is low, it might be necessary to open the damper 44 slightly by throttling the damper 51.

The introduction of the recirculated gas into the furnace at the openings 79 has a number of unobvious advantages which makes it particularly effective with the type of furnace shown. Cases leaving the lower portion 28 of the combustion chamber are restricted to the area between the abutments 19 and 23 and flow into the upper portion 29 of the combustion chamber along lines which are distinctly separated from the forward wall 14 and the rearward of the furnace. The main effect of this is that any slag particles which reside in the gas flow have a good opportunity to cool OE and form hard particles before they strike any heat exchange surface. The tendency of this type of furnace is to keep the gases away from the front and rear walls until such cooling takes place. This separation or stratification of the gases away from the walls cooperates with the function of almost complete combustion in the lower portion 28 to produce a very clean furnace. It has the effect also of providing for a greater uniformity of furnace temperature across the superheater and reheater and makes possible a smaller furnace height. Now, when the recirculated gas is introduced through the opening 69 in the lower surface of the abutments, the normal position of the vanes 93 would be upward, whereas the vanes 85 and 87 of the burners will be inclined downwardly into the high-temperature lower portion 28. The recirculated gas thus introduced through the opening 79 passes outwardly around the noses 19 and 23 and further accentuates the separation of the main body of the products of combustion in these walls. It might be said that the recirculated gases form an insulating blanket between the main products of combustion and the front and rear walls, thus producing the effect of less slagging and fouling of the water walls. At the upper portion of the furnace the reversal of gas direction by the nose 4'1 and horizontal pass 42 produces sufiicient mixing of the recirculated gases and the main product of combustion to accomplish the increases in mass flow and thorough mixing of gases which is necessary to good control of reheat and superheat. The selection of this particular portion of the furnace for the introduction of recirculated gases has also been beneficial because of the fact that it in no way interferes with combustion. As has been stated above, in the high temperature cell 28 combustion takes place almost entirely below the level of the abutments 19 and 23. Furthermore, the stratification of the recirculated gases adjacent the walls 14 and 15 assures that these gases will mix very little with the main products of combustion until they reach a point well up in the combustion chamber. This means that combustion has a considerable opportunity to take place with the proper mixture of fuel and air long before the recirculated gases are mixed with them.

Certain minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is new and desired to secure by Letters Patent is:

1. Apparatus for controlling superheat and reheat in a steam generating unit, comprising walls defining a vertically-elongated furnace, a back pass through which the products of combustion travel after they leave the furnace, abutments on opposed walls of the furnace, each abutment having inclined upper and lower surfaces intersecting inwardly of the furnace Walls to form a restriction in the furnace, the furnace being provided with a slagging bottom, downwardly-directed burners located on the said lower inclined surfaces of the abutments, a series of openings into the furnace located on the lower surfaces of the abutments and having upwardly inclined directing means, a fan, a first conduit connecting the openings to the fan, a second conduit connecting the fan to the said back pass, a damper regulating gas flow to the openings, at convection superheater, a convection reheater, the superheater and reheater being located downstream of the said openings, the gas flowing from the openings in a direction generally parallel to the said lower surfaces of the abutments to provide protective blankets over the surfaces of the abutments, indicators associated with the superheater and reheater producing signals proportional to the degree of superheat and reheat, an actuator for determining the setting of the damper, the control means receiving the signals from the indicators and transmitting a signal to the actuator to maintain the degree of superheat and reheat at selected predetermined values, the damper opening and closing to increase and decrease the flow of gas through the first conduit to the openings to maintain the temperature of superheat at a predetermined value.

2. Apparatus for controlling superheat in a steam generating unit, comprising walls defining a vertically-elongated furnace, a back pass through which the products of combustion travel after they leave the furnace, abutments on opposed walls, each abutment having inclined upper and lower surfaces intersecting inwardly of the furnace walls to form a restriction in the furnace, the furnace being pnovided with a slagging bottom, directional flame burners having downwardly inclined vanes located on the said lower inclined surfaces of the abutments, a series of openings into the furnace located on the lower surfaces of the abutments between the burners, the openings having upwardly inclined vanes, a first conduit connected at one end to the openings, a fan whose outlet is connected to the other end of the conduit, a second con-.

duit connecting the inlet of the fan to the said back pass, means for regulating gas flow to the openings, the gas flowing from the openings in a direction generally parallel to the said lower surfaces of the abutments to provide protective blankets over the surfaces of the abutments, a convection superheater located downstream of the said openings, an indicator associated with the superheater producing a signal representative of the degree of superheat, an actuator for determining the setting of the said means, and control means receiving the signals from the indicator and transmitting a signal to the actuator to main tain the degree of superheat at a selected predetermined Value, means for regulating gas flow increasing and decreasing the flow of gas through the first conduit to the openings to increase and decrease, respectively, the heat transfer to the superheater to maintain the superheat at a predetermined value.

3. Apparatus for controlling superheat in a steam generating unit, comprising walls defining a vertically-elongated furnace, a back pass through which the products of combustion travel after they leave the furnace, abutments on opposed Walls, each abutment having inclined upper and lower surfaces intersecting inwardly of the furnace walls to form a restriction in the furnace, the furnace being provided with a slagging bottom, a series of directional flame burners having vanes which are angularly adjustable about horizontal axes located on the said lower inclined surfaces of the abutments, a series of openings into the furnace located on the lower surfaces of the abutments alternately between the said burners, the openings having vanes which are rotatably adjustable about horizontal axes, a first conduit connected at one end to the openings, a fan whose outlet is connected to the other end of the conduit, a second conduit connecting the inlet of the fan to the said back pass, means for regulating the gas flow to the openings, the gas flowing from the openings in a direction generally parallel to the said lower surfaces of the abutments to provide protec tive blankets over the surfaces of the ahutments, a convection superheater located downstream of the said openings, an indicator associated with the superheater producing a signal representative of the degree of superheat, an actuator for determining the setting of the said means, control means receiving the signal from the indicator and transmitting a signal to the actuator to maintain the degree of superheat at a selected predetermined value, the means for regulating the gas flow to the openings operating to increase or decrease the flow of gas through the first conduit to the openings to maintain the temperature of superheat at a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,851,018 Heller Sept. 9, 1958 2,853,059 Craig Sept. 23, 1958 2,860,613 Heller et a1 Nov. 18, 1958 2,926,636 Paulison Mar. 1, 1960 

2. APPARATUS FOR CONTROLLING SUPERHEAT IN A STEAM GENERATING UNIT, COMPRISING WALLS DEFINING A VERTICALLY-ELONGATED FURNACE, A BACK PASS THROUGH WHICH THE PRODUCTS OF COMBUSTION TRAVEL AFTER THEY LEAVE THE FURNACE, ABUTMENTS ON OPPOSED WALLS, EACH ABUTMENT HAVING INCLINED UPPER AND LOWER SURFACES INTERSECTING INWARDLY OF THE FURNACE WALLS TO FORM A RESTRICTION IN THE FURNACE, THE FURNACE BEING PROVIDED WITH A SLAGGING BOTTOM, DIRECTIONAL FLAME BURNERS HAVING DOWNWARDLY INCLINED VANES LOCATED, ON THE SAID LOWER INCLINED SURFACES OF THE ABUTMENTS, A SERIES OF OPENINGS INTO THE FURNACE LOCATED ON THE LOWER SURFACES OF THE ABUTMENTS BETWEEN THE BURNERS, THE OPENINGS HAVING UPWARDLY INCLINED VANES, A FIRST CONDUIT CONNECTED AT ONE END TO THE OPENINGS, A FAN WHOSE OUTLET IS CONNECTED TO THE OTHER END OF THE CONDUIT, A SECOND CONDUIT CONNECTING THE INLET OF THE FAN TO THE SAID BACK PASS, MEANS FOR REGULATING GAS FLOW TO THE OPENINGS, THE GAS FLOWING FROM THE OPENINGS IN A DIRECTION GENERALLY PARALLEL TO THE SAID LOWER SURFACES OF THE ABUTMENTS TO PROVIDE PROTECTIVE BLANKETS OVER THE SURFACES OF THE ABUTMENTS, A CONVECTION SUPERHEATER LOCATED DOWNSTREAM OF THE SAID OPENINGS, AN INDICATOR ASSOCIATED WITH THE SUPERHEATER PRODUCING A SIGNAL REPRESENTATIVE OF THE DEGREE OF SUPERHEAT, AN ACTUATOR FOR DETERMINING THE SETTING OF THE SAID MEANS, AND CONTROL MEANS RECEIVING THE SIGNALS FROM THE INDICATOR AND TRANSMITTING A SIGNAL TO THE ACTUATOR TO MAINTAIN THE DEGREE OF SUPERHEAT AT A SELECTED PREDETERMINED VALUE, MEANS FOR REGULATING GAS FLOW INCREASING AND DECREASING THE FLOW OF GAS THROUGH THE FIRST CONDUIT TO THE OPENINGS TO INCREASE AND DECREASE, RESPECTIVELY, THE HEAT TRANSFER TO THE SUPERHEATER TO MAINTAIN THE SUPERHEAT AT A PREDETERMINED VALUE. 